In a typical cellular radio system, mobile terminals communicate via a radio access network (RAN) to one or more core networks. The mobile terminals can be such stations as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access networks.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the mobile terminals within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UMTS is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM). UTRAN is essentially a radio access network providing wideband code division multiple access (WCDMA) to mobile terminals. The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM-based radio access network technologies.
In today's wireless wide area networks, like WCDMA networks, the common transport channels in the downlink, i.e. Paging Channel (PCH), Forward Access Channel (FACH) and Broadcast Channel (BCH), are statically mapped onto physical channels such as Primary Common Control Physical Channel (P-CCPCH) and Secondary Common Control Physical Channel (S-CCPCH) that consume codes and power. The codes are statically assigned to the channels and a normal implementation is that the power cannot be reused for other channels. The BCH is mapped onto the P-CCPCH, whereas the PCH and the FACH are mapped onto the S-CCPCH.
The BCH is used to carry the Broadcast Control Channel (BCCH). BCCH is a logical channel that carries system information, i.e. information on where other common channels are mapped. Thus, the BCCH carries information, e.g., on where the S-CCPCH is located and which of those are carrying FACH, PCH or both. Furthermore, the BCCH carries information on where a High Speed Downlink Shared Channel (HS-DSCH) and its corresponding control channels are mapped. Thus, BCCH, BCH and P-CCPCH are necessary channels that cannot be changed.
The S-CCPCH on the other hand carries PCH and/or FACH. On PCH the paging control channel (PCCH) is mapped. PCCH is used to carry paging messages from a radio resource control protocol (RRC). The FACH is used to carry Common Control Channel (CCCH), Common Traffic Channel (CTCH), Dedicated Control Channel (DCCH) and Dedicated Traffic Channel (DTCH). In addition, FACH is also used to carry Multimedia Broadcast Multicast Services (MBMS) related channels such as MBMS point-to-multipoint Control Channel (MCCH), MBMS point-to-multipoint Traffic Channel (MTCH) or MBMS point-to-multipoint Scheduling Channel (MSCH) and Broadcast Control Channel (BCCH) for mobile terminals or user equipment units in CELL_FACH state. CCCH is used by RRC to communicate with terminals that do not have a cell specific Id (a MAC Id). The identity of the terminal is then carried within the RRC message. CTCH is used for Cell Broadcast Services (CBS). DCCH mapped on FACH is used by RRC to communicate with terminals that have a cell specific Id (a MAC Id). DTCH mapped on FACH is a user plane data transfer channel used by a terminal that has a cell specific Id. DCCH and DTCH can also be mapped onto DCH and HS-DSCH. While it is possible to avoid mapping of DCCH and DTCH onto the FACH in an implementation of the WCDMA standard it has previously been necessary to keep the FACH due to the CCCH, CTCH and the MBMS services.
According to the WCDMA standard these various logical channels are thus mapped onto transport channels that are then transmitted to mobile terminals or user equipment units via physical channels. This mapping is according to the WCDMA standard provided through a number of MAC layer mapping units or MAC entities provided in a so-called MAC layer.
FIG. 1 shows a block schematic of a MAC architecture according to this known principle. In the figure there is shown a first mapping unit 10 or MAC entity, which in WCDMA is denoted MAC-c/sh/m. This first mapping unit 10 is connected to RCC units (not shown) provided in an upper layer of the control structure from where it also receives data in the logical channels PCCH, BCCH, CCCH, CTCH, SHCC, MCCH, MSCH and MTCH. Here SHCCH is a Shared Channel Control Channel. The first mapping unit 10 maps these logical channels onto various transport channels PCH, FACH, RACH, USCH and DSCH in order to be carried on various physical channels, like P-CCPCH and S-CCPCH. In order to do this it furthermore receives control signals MAC CTRL from the upper layers of the structure. Here control is indicated by a dashed line originating from upper layers.
There is furthermore a second mapping unit 12, also often denoted MAC-hs, which is responsible for mapping various logical channels onto HS-DSCH and also for the management of the physical resources allocated to HS-DSCH. In order to do this it also receives control signals MAC CTRL from the upper layers of the structure. The logical channels mapped here are normally used for downlink transfer of data. The second mapping unit 12 also provides associated downlink signaling DL S and associated uplink signaling UL S with mobile terminals on associated signaling channels. Here the signaling is indicated with dashed lines.
In the same way there is a third mapping unit 14, also often denoted MAC-e, which is responsible for scheduling logical channels on Enhanced Dedicated Transport Channels (E-DCH). There is here one third mapping unit 14 per mobile terminal that is communicating with the WCDMA network. In order to perform this scheduling the third mapping unit 14 receives control signals MAC CTRL from the upper layers of the structure together with schedule requests from mobile terminals. Also here there is provided associated downlink signaling DL S and associated uplink signaling UL S with mobile terminals on associated signaling channels. E-DCH is with advantage provided for uplink transfer of data. Also here is the signaling indicated with dashed lines. HS-DSCH is thus used for downlink communication, while E-DCH is used for uplink communication.
There is furthermore a fourth mapping unit 16 provided on a mobile terminal per mobile terminal basis, also denoted MAC-d responsible for mapping logical traffic related channels such as Dedicated Traffic Channels (DTCH) and Dedicated Control Channel (DCCH), onto transport channels Dedicated Channels DCH. In order to do this the fourth mapping unit 16 also receives control signals MAC CTRL from the upper layers of the structure.
There is finally a fifth mapping unit 18, also denoted MAC-es and provided on a mobile terminal per mobile terminal basis. This unit 18 handles E-DCH functionality not covered by the third mapping unit 14. Also the fifth mapping unit 18 receives control signals MAC CTRL from the upper layers of the structure.
In FIG. 1 there is furthermore indicated an Iur interface between the first mapping unit 10 and the fourth and fifth mapping units 16 and 18 as well as an Iub interface between the first mapping unit 10 and the second and third mapping units 12 and 14. Thus it is clear that the first mapping unit 10 may be provided in an RNC, the fourth and fifth mapping units may be provided in another RNC and the second and third mapping units 12 and 14 may be provided in a Node-B. Node-B is another term used for a base transceiver station or base station.
Regarding paging in a WCDMA network, a RRC (Radio Resource Control) paging message is used to wake up terminals from sleep mode in Idle, URA_PCH (UTRAN Registration Area_Paging Channel) and CELL_PCH (Cell_Paging Channel) states. The RRC paging message is sent on a Paging Control Channel (PCCH). A Paging Control Channel PCCH is a logical channel that is mapped onto the physical Paging Channel (PCH).
Terminals are divided into different paging groups in order to achieve a power saving for the terminals. At a specific time occasion in discontinuous reception cycle, a so-called DRX cycle of the paging group, the terminals in the paging group wake up and check whether there is paging information to the paging group. A terminal checks that on a paging indicator channel (PICH).
Hence, a terminal in idle, Cell_PCH or URA_PCH state can receive one PCCH, one PCH and one S-CCPCH at regular intervals. Prior to receiving S-CCPCH, the terminal checks the Paging Indicator Channel (PICH) to see if there is a paging message for its paging group on the PCH. Thus a terminal does not listen to the S-CCPCH continuously but at regular intervals controlled by its DRX cycle.
In WCDMA there may be more than one S-CCPCH used for PCH/PCCH. All S-CCPCHs carrying PCH/PCCH are indicated by means of system information on the Broadcast Control Channel (BCCH). The paging groups are spread out over the different S-CCPCHs. The terminal selects its paging group according to a well defined rule based on the International Mobile Subscriber Identity (IMSI). Thus each terminal only listens for paging information on one S-CCPCH.
It has been perceived that in the existing WCDMA-system architecture every S-CCPCH consumes power and codes that are statically allocated by a Radio Network Controller (RNC). Thus the power and codes cannot be reused for other traffic than the S-CCPCH resulting in an inefficient use of resources. This is especially the case if there are few mobile terminals in a cell.
If there were a way to map the logical channels that today use FACH onto some other channel, FACH could be avoided. However, it is not only FACH that uses S-CCPCH. Also PCH does that. Hence one needs to be able to map PCCH onto some other channel than PCH to be able to avoid S-CCPCH and thus save codes and power.